Process for solubilizing monovalent metal carbonates in oil



United States Patent PROCESS FOR SOLUBILIZING MONOVALENT METAL CARBQNATES IN ()llL Henry W. Anderson, Edwardsville, ill., and Hyman Ratner, Berkeley, Calif., and Grant E. Warren, deceased, late of Martinez, Calit., by Eleanorc R. Warren, executrix, Martinez, Calif, assignors to Shell Development Company, New York, N .Y a corporation of Delaware No Drawing. Application August 16, 1956 Serial No. 604,573

4 Claims. (Cl. 252-33.4)

This invention relates to a method for solubilizing alkali metal carbonates in oil.

In the operation of internal combustion motors it has been found that various highly undesirable by-products of the combustion of the fuel make their way into the portions of the motor immediately adjacent to the combustion zone and into the lubrication system of the motor. A substantial proportion of these by-proclucts are acidic materials resulting from incomplete combus tion of the fuel and/or combustion and/or decomposition of foreign materials, such as sulfur compounds, in the fuel. These acidic by-products are highly corrosive to materials commonly used in the construction of internal combustion motors and cannot be tolerated in the motor.

It has been found that inorganic alkali metal carbonates are excellent additives for compositions used for lubricating internal combustion motorssuch as diesel motorswhich customarily use fuels having a high sulfur content. Such carbonates efliciently neutralize the acidic by-products of the combustion of the fuel used inthe motor, and both the carbonates themselves and the salts they form with the acidic combustion by-prodnets are quite inert with respect to other materials used in the lubricating compositions, do not have any deleterious effect upon the lubricating qualities of the base oils used in the lubricating compositions, and are substantially non-corrosive to metals ordinarily used in the construction of internal combustion motors. However,

alkali metal carbonates are quite oil-insoluble, so that they tend to settle out of the lubricating compositions during periods in which the motor is not operating, forming. sludges, so that these carbonates per se cannotpractically be used as additives for compositions used for lubricating internal combustion motors.

We'have now discovered that alkali metal carbonates may be solubilized-that is, made completely and permanently oil-solubleby forming the carbonate in situ in the presence of an oil-soluble alkali metal salt of an organic acid under certain conditions. The process which embodies this discovery and which is described in detail hereinafter results in solubilization. of at least two equivalents of. alkali metal carbonate per equivalent of solubilizer and in most cases a number of equivalents of carbonate solubilized per equivalent of solubilizer is even greater. These solubilized carbonates are excellent additives for lubricating compositions, for not only do they ef ficiently neutralize the acidic by-products of the combustion ofthe fuel burned in the motor in which the lubricating composition is used, they (due in part to the presence of the salt of the organic acid used as solubilizer.) also act as detergents and peptizing agents improving: the cleanliness of. the motor and preventing formation of. lacquer-like deposits, carbon deposits, sludges and the like from other byproducts of combustion of the motor filell' Briefly, we have found that large amounts of alkali metal'carbbnates are solubilized in oil by forming the carbonate from its constituent ions in the presence of about 50% or less, on an equivalent basis, of an oilsoluble alkali metal salt of an organic acid of the group consisting of the oil-soluble petroleum sulfonic acids and the oil-soluble alkyl-substituted salicylic acids in a liquid reaction medium comprising a substantial amount of a liquid hydrocarbon and a substantial amount of water. In the preferred practice of the process which embodies this discovery, the liquid hydrocarbon is a solvent for the metal salt of the organic acid. Accordingly, alkali metal carbonates are solubilized by dissolving the oilsoluble alkali metal salt of the organic acid in a liquid hydrocarbon adding sufficient water to establish a substantial aqueous phase and thereafter forming in the res'u'lting mixture at least two equivalents of an alkali metal carbonate per equivalent of said salt by adding to the said mixture the hydroxide of the desired alkali metal and thereafter passing carbon dioxide into the entire mixture. 20

Suitable as the salt of the organic acid is the oil-soluble alkali metal salt of any oil-soluble petroleum sulfonic acid or any oil-soluble alkyl-substituted salicylic acid containing at least twelve carbon atoms, and, including both the neutral salts and the moderately basic salts. By oil-soluble salt is meant the salt of the acid having a substantial solubility in hydrocarbon materials such as benzene, toluene, xylene, mixtures of xylenes, gasoline fractions, lubricating oil fractions, and the like. The salt must be soluble in such hydrocarbon materials to an extent of at least 10% by weight, and preferably, the

solubility of the salt should be greater than 10% by weight-up to 50% by weight or even more. Many alkali metal salts of the aforesaid oil-soluble organic acids are soluble to the extent of from about 15% to about 40% by weight in common hydrocarbon liquids. Such salts are preferred.

In general, such salts are the salts of the organic acids which themselves are soluble in oil at. the levels set out above for the salt.

The alkyl-substituted salicylic acids in which the alkyl groups are each long-chain alkyl groups containing a total of at least about 12 carbon atoms are suitable. The most desirable class of these acids comprises those which have been derived from benzene or phenol which has been alkylated with straight-chain hydrocarbons containing from about 8 to about 26, and preferably from about 10 to about 22 carbon atoms. Alkyl-substituted salicylic acids of the kinds prepared by the processes disclosed in copending application Serial Number 403,445 (filed January 11, 1954), now United States Patent No. 2,807,643,

issued September 24, 1957, are preferred members of this class of carboxylic acids.

The references herein to alkyl salicylic acids are intended to cover the individual acids and also mixtures of acids having dilferent alkyl substituents, for example,a

mixture of alkyl salicylic acids having alkyl groups containing from about 14 to about 22 carbon atomsfor example a mixture of C -C monoand di-alkyl salicylic acids. Mixtures of such acids, normally containing some of the corresponding phenates and phenols, will generally be used in practice, and in many cases are to be preferred.

The various oil-soluble petroleum sulfonic acids, particularly petroleum sulfonic acids whichare obtained by sulfonating various hydrocarbon fractions, such as lubricating oil fractions, are suitable, these materials being aliphatic-substituted cyclic sulfonic acids in which the aliphatic substituent(s) contain a total of at least 12 carbon atoms.

The term petroleum sulfonic acids is intende'dto cover all sulfonic' acids'which are" derived directly from petroleum products.

The alkali metal salts of these acids which are used as starting materials for the process of this invention may be prepared by directly neutralizing the acid with an alkali metal base. The salt may be the neutral salt or it may be a slightly basic salt of the organic acid. By slightly basic salt is meant the salt prepared by neutralizing the acid with an excess of base and containing more metal than the neutral salt, the added metal being incorporated in the salt through processes involving physical mixing.

Methods for accomplishing the preparation of such salts are well known in the art. The alkali metal of the salt of the organic acid may be the same as that of the alkali metal carbonate solubilized, or the two metals may be different alkali metals. If it is desired that the metal of the solubilizer be the same as the solubilized carbonate, it is often convenient to form the necessary alkali metal salt of the organic acid in situ in the reaction mixture which is to be used in the solubilization of the carbonate-in such a case, the organic acid is itself used as the raw material and an additional amount of the alkali metal hydroxide used to prepare the carbonate is used to neutralize the acid. The solubilized carbonate product formed by performance of the process of the invention may also be used as the starting material for a further cycle of the process of the inventionto increase the amount of carbonate solubilized per equivalent of solubilizer.

As used herein, the term alkali metal refers to the metals of group I of the periodic chart of the elements (Merck and Co., revised, 1955). It is preferred that the salt of the organic acid be the sodium salt, and that sodium hydroxide be used as the alkali metal hydroxide used to form the carbonate, since these sodium compounds are most widely available, and are the cheapest.

The alkali metal carbonate is solubilized by forming it in situ in the presence of the alkali metal salt of the organic acid and in the presence of a liquid reaction medium comprising a substantial amount of water and a substantial amount of a liquid hydrocarbon. Preferably the liquid hydrocarbon is one in which the metal salt of the organic acid is quite soluble.

Such hydrocarbons as benzene, toluene, or xylene are quite suitable, as are mixtures of one or more of these compounds. Gasoline fractions, for example gasoline fractions boiling in the range of from about 100 C. to about 150 C. also are suitable. Mineral oil fractions generally are siutable, provided their viscosity is not too high. It is preferred that the boiling point of the liquid hydrocarbon be less than about 300 C. Lubricating oil fractions having a viscosity of from about 100 to about 400 seconds Saybolt Universal at 38 C. are suitable. It is preferred that the liquid hydrocarbon used be a hydrocarbon boiling in the range of from about 100 to about 200 C.

The amount of liquid hydrocarbon solvent and metal salt should be so chosen that the concentration of the salt in the solvent is at least about by weight. It is preferred that the concentration of the salt in the solvent not exceed about 50% by Weight, since if tooconcentrated a solution is used and the solubilized carbonate is less soluble than the metal salt, precipitation of solubilized carbonate may occur, introducing an undesirable solid phase in the reaction mixture. In general, concentrations of salt in the solvent of from about by weight to about 40% by weight are most desirable.

There must be a substantial aqueous phase in the reaction zone. Thus, the amount of water present in the reaction zone must amount to at least 2% by weight of the total reaction mixture, and it is preferred that the amount of water amount to at least 3% by weight of the reaction mixture. Because all the water present must eventually be removed, it is desirable that the amount of water charged not exceed about 50% by weight of 4 the reaction mixture. In general, it will be found that little advantage occurs by the use of an amount of water in excess of about 20% by weight of the reaction mixture.

The alkali metal hydroxide may be added as such, but preferably is added in the form of a solution or suspension in water. It is preferred that the concentration of the hydroxide in the solution be at least about 10% by weight. In some cases it may be desirable to use highly concentrated solutions of the hydroxide, for example, saturated solutions or solutions containing up to by weight or more of hydroxide. It is most desirable that the concentration of the hydroxide lie within the range of from about 20% to about 60% by weight of the solution. When such solutions are used, due care must be taken to maintain the concentration of water in the reaction zone within the ranges heretofore set out.

The alkali metal carbonate is formed in situ by passing carbon dioxide into the reaction mixture containing free alkali metal hydroxide. Thus, where an alkali metal salt of the acid is used as the raw material, alkali metal hydroxide is added and carbon dioxide passed into the mixture; where the acid itself is the raw material, alkali metal hydroxide is added in an amount sufficient to provide an excess of hydroxide over the amount theoretically required to neutralize the acid. In any case, the amount of hydroxide added is sufiicient to provide at least two equivalents of free hydroxide in the reaction mixture per equivalent of acid charged. It is desirable that the amount of hydroxide charged should be such that when the desired amount of carbonate has been solubilizedrelative to the amount of solubilizer present-an excess of hydroxide exists in the reaction mixture. The ratio of the number of moles of carbon dioxide charged per mole of alkali metal hydroxide charged, at the point where the desired amount of carbonate has been solubilized, must not exceed 1.0 and preferably does not exceed about 0.9. For reasons to be set out in detain hereinafter, it is desirable that the ratio not exceed about 0.85. To insure maximum solubilization of the carbonate economically, however, the carbon dioxide-tohydroxide ratio should be at least 0.5, though in special cases, the ratio may be somewhat lower. Since a small proportion of the carbonate formed will not be solubilized, there should be provided a slight excess of the hydroxide over the amount theoretically needed to form the desired amount of solubilized carbonate. Thus, the

desired amount of solubilized carbonate per unit weight of solubilizer should first be determined; in calculating the amount of hydroxide charged to provide the desired amount of solubilized carbonate, an excess of about 5% (molar) (and not exceed about 15%) should be included to allow for the portion of the carbonate not solubilized. Further, due allowance should be made for providing the necessary carbon dioxide-to-hydroxide mole ratio as previously set out.

The carbon dioxide-to-hydroxide mole ratio must be carefully controlled within the limits set out above because of the existence of a phenomenon which we term overcarbonation. Thus, it has been found that for a. reaction mixture containing a given amount of metal hydroxide, as carbon dioxide is passed into the mixture, the amount of carbonate solubilized gradually increases; then, as the introduction of carbon dioxide continues, the amount of carbonate solubilized suddenly begins to decrease, this phenomenon normally occurring just before the amount of carbon dioxide theoretically required to convert all of the hydroxide to the carbonate has been added. The stability of the solubilized carbonate product-the resistance of the product to precipitation of the metal carbonate during storage and/or in usebegins to decline rapidly at about the same carbon dioxide-to-hydroxide ratio at which the solubilization of the carbonate this phenomenon, its occurence may be prevented by maintaining the carbon dioxide-to-hydroxide mole ratio within the limitsset out hereinbefore and by controlling the rate at which the carbon dioxide is added, and the speed and manner in which the carbon dioxide is introduced into the bulk of the reaction mixture; It should be noted that overcarbonation may be a local as well as a general effect, so that the amount of carbonate solubilized may be reduced substantially by allowing local overcarbonation to occur. Such can be prevented primarily by preventing the local amount of carbon dioxide from exceeding the local amount of base. Etfective dispersal of the gaseous and liquid components of the reactionmixture and correlation of the carbon dioxide addition rate with the degree of such dispersion is essential. Danger of local overcarbonation also is reduced by diluting the carbon dioxide with an inert gas, such as nitrogen, air or water vapor.

Solubilization of the metal carbonate is effected at 'any temperature within the range of from about 150 F. to about 250 l b-temperatures of from about 160 F. to about 225 F. are preferred. By carrying out the process at moderately elevated temperaturese.g., up to about 2 3 atmospheres-correspondingly higher temperatures-may be used without. undue volatilization of the liquid components of the reaction mixture.

The water present in the reaction mixture may be confined to the reaction-zone during the course of the reaction andthen removed, or apart of the water may be removed-during the course of the reaction. Where the latter technique is used, there must remain in the reaction mixture a substantial aqueous phase throughout the course of the reaction. A convenient, and preferred, technique comprises slowly and continuously removing water during the course of the reaction, so that as the reaction nears completion, the amount of water approaches the minimum permissible concentration-Le, about 2% by weigh-t of the reaction mixture. After a further short period to'insure completion of the reaction, the mixture is dehydratede.g., by heating the reaction mixture to -a temperature-of about 280-320 F.- If desired, the mixture may be blown with air to increase the rate of water removal. The product is then filtered to remove any suspended solid materials (mainly metal carbonate and metal hydroxide).

The reaction time is not a critical factor in the process of the invention. In general, a reaction time of at least one-half hour is required, but it seldom exceeds about 4- 5 hours. In most cases, a reaction time of from about one-half to about 2 hours is required.

The process of the invention may be operated in a batch manner, or it may be operated in a cyclic, including continuous, manner. When the process is operated in a cyclic manner, the sludge obtained by filtration of the reaction mixture, which sludge comprises primarily alkali metal carbonate and alkali metal hydroxide, may be used to neutralize the organic acid.

The following examples are olfered as illustrations of specific applications of the process of the invention:

Example I A solution of neutral lithium sulfonates in a lubricating oil fraction was prepared by treating a commercial sodium salt of petroleum sulfonic acids twice with a two-fold excess of lithium chloride (the lithium chloride being provided as a 30% by weight aqueous solution) and removing the Water and the sodium chloride formed. 1000 grams of the oil solution of neutral lithium sulfonates thus prepared, containing 770 grams of oil and 230 grams of the lithium sulfonate were mixed with 78 grams of lithium hydroxide and 156 grams of water. The mixture was heated to 200 F. and with constant thorough stirring, 65 grams of carbon dioxide were added over a period of 120 minutes. The mixture was then dried by heating the mixture at 320 F., and was filtered'hot -to remove solid materials present. A product containing 4.40 equivalents of lithium carbonate per equivalent" ofneutral lithium sulfonate was obtained.

Example [I 360 grams of the neutral sodium salt of petroleum sulfonic acids was mixed with 1287 grams of a lubricating oil fraction. 150 grams of sodium hydroxide and 75 grams of water were added, and the mixture heated to 215 F. While the mixture was maintained at this temperature and while it was being thoroughly agitated, 72 grams of carbon dioxide were added over a period of 120 minutes. A small portion of the mixture was then dried at 310 F-., and filtered to give a product having a base number of 27 (the base'number of the neutral salt used as starting material was 0.0)

Example 111 To demonstrate that the solubilized carbonate of this nature would be suitable as starting material in the process of this invention, and to demonstrate that the product obtained from such a starting material contained more solubilized carbonate per equivalent of solubilizer, the crude product in Example II was heated to dryness at 300 F., decanted and reacted in the following manner: 1148 grams of the anhydrous product were mixed with 200 grams of sodium hydroxide and 50 milliliters of water, the mixture was heated to 210 F., and with constant stirring of the mixture, 64 grams of carbon dioxide were passed into the mixture over a period of 90 minutes.

A dried and filtered test portion of the product had a base numberof'45.

The crude'product was again decanted and dried. 650 grams of the anhydrous product were mixed with 200 gramslof sodium hydroxide and 50 milliliters of water, the mixture was heated to a temperature of 210 F. and 40 grams of carbon dioxide were passed into the heated and agitated mixture over a period of 75 minutes. The product was dehydrated and filtered. The base number of the final product was 58.

Example IV Repetition of the experiment described in Example I, but substituting for the neutral lithium sulfonate an equivalent amount of a neutral lithium salt of a C -C -alkylsubstituted salicyclic acid results in a product containing substantially the same number of equivalents of lithium carbonate per equivalent of solubilizer as were contained in the product of Example I.

1 Example V 1650 grams of a 22% by weight solution of neutral sodium petroleum sulfonates in a lubricating oil fraction was mixed with 200 grams of sodium hydroxide and grams of water. The mixture was heated to 205 F., and 40 grams of carbon dioxide were passed into the heated, agitated mixture over a period of 1 hour. The product contained 2.1 equivalents of sodium carbonate per equivalent of neutral sodium sulfonate.

The term base number means total base number as determined by electrometric titration according to ASTM designation D664-49. By this test, metal hydroxide and metal salts of weak volatile acids, such as carbonic acid, have equal alkalinity on a mole-for-mole basis.

Example VI Repetition of the experiment of Example I, in each replicate changing one process variable to determine the elfect of that variable on the desired reaction sets out the following facts:

(a) If no carbon dioxide is charged, but a small amount of the monovalent metal hydroxide is solubilized;

(b) If solid metal carbonate, preformed outside the reaction zone, is used, rather than being formed in situ in '7 the reaction zone, no solubilization of the carbonate occurs.

(c) If the reaction of the metal hydroxide and carbon dioxide is carried out in the absence of water, no carbonate is solubilized.

The solubilized carbonates obtained by performance of the process of this invention are suitable for all uses wherein an oil-soluble material containing a high proportion of carbonate-Le, material capable of neutralizing acidsis desirable. The amount of the solubilized carbonate added to the lubricant depends upon several factors, but primarily the criterion for determining the amount of carbonate added is that suflicient should be added to effect neutralization of all of the acids which ,are expected from combustion of the fuel used, based on the effective life of the lubricant. Of course, additional amounts of the carbonate may be added to the lubricant from time to time as necesary to give the desired eflect.

The solubilized carbonates prepared according to the process of this invention may be used in lubrcating oils in widely varying concentrations. In general, the carbonate will be used in lubricating oils in concentrations between 0.1 and 15% by weight. If desired, the carbonate may be combined with other additives, for instance anti-oxidants and BF. dopes (viz. extreme pressure dopes, additives which render the lubricating oils suitable for use at very high pressures).

The solubilized carbonates prepared according to the invention may in some cases also be used to advantage in hydrocarbon oils other than lubricating oils. For example, they are suitable for use in fuel oils where they have the effect of counteracting clogging of pumps, filters' and similar apparatus, and in light hydrocarbon mixtures which are used as anti-corrosives. The solubilized carbonate may also be used in preparing lubricating greases.

We claim as our invention: 1. A process for solubilizing an alkali metal carbonate in a liquid hydrocarbon, said process comprising bringing together an alkali metal hydroxide and carbon dioxide to form an alkali metal carbonate only in situ in the presence of only a liquid reaction medium consisting cssentially of a liquid hydrocarbon boiling below about 300 0, water and an organic acid compound dissolved in said liquid hydrocarbon, containing at least 12 carbon atoms, and selected from the group consisting of (l) petroleum sulfonic acids, (2) alkyl-substituted salicyclic acids, and (3) alkali metal salts of such acids, the amount of water being at least 2% of the weight of said reaction medium, and thereafter removing the water.

2. A process according to claim 1 wherein the amount of carbon dioxide charged is such that less than all of the monovalent metal hydroxide is converted to the carbonate.

3. A process for solubilizing an alkali metal carbonate in a liquid hydrocarbon, said process comprising bringing together an alkali metal hydroxide and carbon dioxide to form an alkali metal carbonate only in situ, in the presence of only a liquid hydrocarbon boiling below 300 C. and containing dissolved therein from about 10% to about by weight thereof of an alkali metal salt of a petroleum sulfonic acid, and in the presence of water in an amount of at least 2% of the weight of the solution of the salt, and thereafter removing the water.

4. A process for solubilizing an alkali metal carbonate in a liquid hydrocarbon, said process comprising bringing together an alkali metal hydroxide and carbon dioxide to form an alkali metal carbonate only in situ in the presence of only a liquid hydrocarbon boiling below 300 C. and containing dissolved therein from about 10% to about 50% by weight thereof an alkali metal salt of an alkyl-substituted salicyclic acid containing at least 12 carbon atoms, and in the presence of water in an amount of at least 2% of the weight of the solution of the salt, and thereafter removing the water.

References Cited in the tile of this patent UNITED STATES PATENTS Schuessler May 7, 1957 

1. A PROCESS FOR SOLUBILIZING AN ALKYL METAL CARBONATE IN A LIQUID HYDROCARBON, SAID PROCESS COMPRISING BRINING TOGETHER AN ALKALI METAL HYDROXIDE AND CARBON DIOXIDE TO FORM AN ALKALI METAL CARBONATE ONLY IN SITU IN THE PRESENCE OF ONLY A LIQUID REACTION MEDIUM CONSISTING ESSENTIALLY OF A LIQUID HYDROCARBON BOILING BELOW ABOUT 300*C., WATER AND AN ORGANIC ACID COMPOUND DISSOLVED IN SAID LIQUID HYDROCARBON, CONTAINING AT LEAST 12 CARBON ATOMS, AND SELECTED FROM THE GROUP CONSISTING OF(1) PETROLEUM SULFONIC ACIDS, (2) ALKYL-SUBSTITUTED SALICYCLIC ACIDS, AND (3) ALKALI METAL SALTS OF SUCH ACIDS, THE AMOUNT OF WATER BEING AT LEAST 2% OF THE WEIGHT OF SAID REACTION MEDIUM, AND THEREAFTER REMOVING THE WATER. 